It is well known that in pulse doppler radar, the choice of low PRF (pulse repetition frequency) yields an unambiguous range capability and a relaxed dynamic range requirement, but results in blind speeds, and velocity ambiguities. Existing radars tend to live with the blind speeds, and generally rely on scan-to-scan range changes in order to measure target velocity. In a radar designed so that rapid PRF changes can be effected, some of the disadvantages of low PRF operation can be eliminated. In defining appropriate PRF's and subsequent processing, one would strive for a processor architecture which has the capability to (1) eliminate blind speeds, (2) accurately measure target radial velocity and resolve velocity ambiguities, and (3) effect noncoherent integration gain using the individual PRF outputs. The multiple PRF processor system described herein not only offers these capabilities, but additionally provides other performance benefits which are both interesting and important.
A basic PRF chosen to provide a predetermined unambiguous range coverage in airborne target search has associated with it blind speeds that repeat at the basic PRF interval. At UHF, a PRF of 320 Hz, for example, corresponds to a velocity of 218 kts. Assuming that the blind speeds due to Moving Target Indication (MTI) processing are 80 Hz or 25% wide, this results in 55 kt blind speeds that repeat at 218 kt intervals.